Various constructions and techniques will be described below. However, nothing described herein should be construed as an admission of prior art. To the contrary, Applicants expressly reserve the right to demonstrate, where appropriate, that anything described herein does not qualify as prior art under the applicable statutory provisions.
The term “nanostructure” material is used by those familiar with the art to designate materials including nanoparticles such as C60 fullerenes, fullerene-type concentric graphitic particles, metal, compound semiconductors such as CdSe, InP; nanowires/nanorods such as Si, Ge, SiOx, GeOx, or nanotubes composed of either single or multiple elements such as carbon, BxNy, CxByNz, MoS2, and WS2. One of the common features of nanostructure materials is their basic building blocks. A single nanoparticle or a carbon nanotube has a dimension that is less than 500 nm at least in one direction. These types of materials have been shown to exhibit certain properties that have raised interest in a variety of applications and processes.
Nanostructures, such as carbon nanotubes, are known to be excellent electron field emitters due to their unique geometry, extremely high mechanical strength, and good chemical and thermal stability. Experiments have shown that they have a low threshold field for electron emission (˜1-2V/μm) and are capable of emitting at very high current densities.
However, due to materials issues such as poor film uniformity and insufficient adhesion and electrical conductivity between carbon nanotubes and the substrate, high stable emission current has not been obtained from macroscopic carbon nanotube-containing structures and devices, which has limited their practical utilization.
Among all the available techniques for synthesizing carbon nanotubes, laser-ablation and arc-discharge methods produce carbon nanotubes with a high level of structural perfection and therefore amongst the best electron field-emission properties. However, materials made therefrom are in the form of either porous membranes or powders that are not easily incorporated into field-emission devices such as cathodes, and therefore cannot be used directly on devices without further processing. Although the chemical vapor deposition (CVD) methods can grow carbon nanotubes directly on substrates, they require very high temperatures (600-1000° C.) and a reactive environment. Also, CVD grown carbon nanotubes generally do not have the same level of structural perfection and, as a result, lack the same emission properties as the tubes made by laser-ablation or arc-discharge methods. To fully utilize the excellent electron field-emission properties of carbon nanotubes, especially single wall carbon nanotubes made by laser-ablation and arc-discharge methods, some deposition techniques have been developed.
In addition, the nanotubes contained in powders or soot formed by laser-ablation and arc-discharge methods are randomly oriented. However, when utilized as sources for electron emission, it is advantageous to orient the tips of the nanotubes in the same direction, such as toward a common emission target. Thus, the normal lack of orientation of the nanotubes presents and additional challenge to their utilization in field-emission devices.
Representative disclosures of nanostructure containing materials, devices and techniques include the following.
U.S. Pat. No. 6,630,772 (based on U.S. patent application Ser. No. 09/296,572 entitled “Device Comprising Carbon Nanotube Field Emitter Structure and Process for Forming Device”), the disclosure of which is incorporated herein by reference, in its entirety, discloses a carbon nanotube-based electron emitter structure.
U.S. patent application Ser. No. 09/351,537, now abandoned, entitled “Device Comprising Thin Film Carbon Nanotube Electron Field Emitter Structure”, the disclosure of which is incorporated herein by reference, in its entirety, discloses a carbon nanotube field emitter structure having a high emitted current density.
U.S. Pat. No. 6,553,096 entitled “X-Ray Generating Mechanism Using Electron Field-Emission Cathode”, the disclosure of which is incorporated herein by reference, in its entirety, discloses an x-ray generating device incorporating a cathode formed at least in part with a nanostructure-containing material.
U.S. Patent Application Publication No. US-2002/0094064, entitled “Large-Area Individually Addressable Multi-Beam X-Ray System and Method of Forming Same”, the disclosure of which is incorporated herein by reference, in its entirety, discloses structures and techniques for generating x-rays which includes a plurality of stationary and individually electrically addressable field emissive electron sources.
U.S. Pat. No. 7,085,351 (based on U.S. patent application Ser. No. 10/358,160 entitled “Method and Apparatus for Controlling Electron Beam Current”), the disclosure of which is incorporated herein by reference, in its entirety, discloses an x-ray generating device which allows independent control of the electron emission current by piezoelectric, thermal, or optical means.
U.S. Patent Application Publication No. US-2002/0140336, entitled “Coated Electrode with Enhanced Electron Emission and Ignition Characteristics”, the disclosure of which is incorporated herein by reference, in its entirety, discloses a coated electrode construction which incorporates nanostructure-containing materials.
U.S. Patent Application Publication. No. US-2004/0240616 (based on U.S. patent application Ser. No. 10/448,144, now abandoned, entitled “Nanomaterial Based Electron Field-Emission Cathodes for Vacuum and Gaseous Electronics”), the disclosure of which is incorporated herein by reference, in its entirety, discloses electronics incorporating field-emission cathodes based at least in part on nanostructure-containing materials.
U.S. Pat. No. 6,385,292 entitled “Solid State CT System and Method”, the disclosure of which is incorporated herein by reference, in its entirety, disclose an x-ray source including a cathode formed from a plurality of addressable elements.
U.S. Patent Application Publication No. US-2004/0256975 (based on U.S. patent copending application Ser. No. 10/464,440, entitled “Improved Electrode and Associated Devices and Methods”), the disclosure of which is incorporated herein by reference, in its entirety, discloses a device including cathode incorporating a nanostructure-containing material embedded in a matrix material.
Therefore, processes which can readily incorporate carbon nanotubes, or other nanostructure-containing materials, formed by arc-discharge, laser ablation techniques, and the like, into adherent robust field emission devices while provide good electrical conductivity and a substantial number of nanotubes protruding toward the emission direction are desired.